Numerous methods and apparatus exist for separating components from a fluid stream containing gases, liquids and/or solids. Conventional separation apparatuses include distillation columns, stripping columns, filters and membranes, centrifuges, electrostatic precipitators, dryers, chillers, cyclones, vortex tube separators, and absorbers. These methods and devices are relatively ineffective and/or inefficient in separating gas components of gaseous mixtures.
For example, a commonly utilized system and method for separation of hydrogen sulfide (H2S) or carbon dioxide (CO2) from a gas stream involves using a series of stripping columns to absorb target gaseous components into a solvent/reactant followed by the distillation of the solvent/reactant to recover the target gas components. The equipment involved usually requires a large footprint due to the numerous pieces of process equipment needed for such a separation scheme. Such a process may also suffer from high energy consumption requirements and solvent/reactant loss during operation.
A conventional amine plant exemplifies the requirements of an absorption/distillation sequence used to remove a target component from a gas stream. In general, this process involves contacting a gas stream comprising a target component with a reactant in a stripping column. The gas removed from the stripping column is clean gas with the majority of the target component removed. The reactant is conventionally an amine that forms a complex with a target component such as carbon dioxide. The target-component enriched complex then passes to a regenerator tower, which may be a stripping column or distillation tower, where the complex is heated to release the target component. Additional equipment required to operate the amine unit typically includes flash tanks, pumps, reboilers, condensers, and heat exchangers. When the gas stream contains too high of a target component concentration, the energy required to remove the target component may exceed the useful chemical energy of the stream. This limitation sets an upper concentration level of the target component at which the process can be economically operated. This process also suffers from a high energy consumption, solvent loss, and a large footprint, making the process impracticable for offshore use.
Separation of gaseous components of a gas mixture has also been effected by contacting the gas mixture with selectively permeable filters and membranes. Filtration and membrane separation of gases include the selective diffusion of one gas through a membrane or a filter to effect a separation. The component that has diffused through the membrane is usually at a significantly reduced pressure relative to the non-diffused gas and may lose up to two thirds of the initial pressure during the diffusion process. Thus, filters and membrane separations require a high energy consumption due to the energy required to re-compress the gas diffused through the membrane and, if the feed stream is at low pressure, the energy required to compress the feed stream to a pressure sufficient to diffuse one or more feed stream components through the membrane. In addition, membrane life cycles can vary due to plugging and breakdown of the membrane, requiring additional downtime for replacement and repair.
Centrifugal force has been utilized to separate gaseous components from gas-liquid feed streams. For example, cyclones utilize centrifugal force to separate gaseous components from gas-liquid fluid flows by way of turbulent vortex flow. Vortices are created in a fluid flow so that heavier particles and/or liquid droplets move radially outward in the vortex, thus becoming separated from gaseous components. Within a cyclone, the gas and liquid feed stream flow in a counter-current flow during separation such that the heavier components and/or liquid droplets are separated from the gaseous components by gravity in a downward direction after the initial separation induced by the vortex while the gaseous components are separated in the opposite direction. Considerable external energy must be added to cyclones to achieve effective separation.
U.S. Pat. No. 6,524,368 (Betting et al.) refers to a supersonic separator for inducing condensation of one or more components followed by separation. Betting is directed to the separation of an incompressible fluid, such as water, from a mixture containing the incompressible fluid and a compressible fluid (gas). In this process, a gas stream containing an incompressible fluid and a compressible fluid is provided to a separator. In the separator, the gas stream converges through a throat and expands into a channel, increasing the velocity of the gas stream to supersonic velocities, inducing the formation of droplets of the incompressible fluid separate from the gas stream (and the compressible fluid therein). The incompressible fluid droplets are separated from the compressible fluid by subjecting the droplets and the compressible fluid to a large swirl thereby separating the fluid droplets from the compressible fluid by centrifugal force. The system involves a significant pressure drop between the inlet and outlet streams, and a shock wave occurs downstream after the separation, which may require specialized equipment to control.
It has been proposed to utilize centrifugal force to separate gas components from a gaseous mixture. In a thesis by van Wissen (R. J. E. VAN WISSEN, CENTRIFUGAL SEPARATION FOR CLEANING WELL GAS STREAMS: FROM CONCEPT TO PROTOTYPE (2006)), gas centrifugation is described for separating two compressible fluids in the absence of an incompressible fluid. The separation is carried out using a rotating cylinder to create a plurality of compressible streams based on the difference in the molecular weight of the gaseous components. As noted in the thesis, the potential to separate compressible components such as carbon dioxide from light hydrocarbons is limited by the differences in molecular weights between the components. As such, centrifuges cannot provide a highly efficient separation when the component molecular weights are close to one another. Such a design also suffers from an extremely low separation throughput rate that would require millions of centrifuges to handle the output of a large gas source.
What is needed is a separation apparatus and method that provides high separation efficiency of compressible components while avoiding or reducing pressure drop, and the need to supply large amounts of external energy.